feat(discovery-core): add hash primitives and outgoing channel storage slots

[m-kus]

Add Privacy Pool Cryptographic Primitives

This PR adds several cryptographic primitives needed for the privacy pool implementation:

1. Adds new domain separation tags for:

   • Nullifier derivation
   • Channel key derivation
   • Channel and subchannel marker derivation
   • Outgoing channel ID derivation
   • Encrypted recipient address

2. Implements hash functions for:

   • Computing nullifiers
   • Deriving channel keys
   • Computing channel and subchannel markers
   • Computing outgoing channel IDs
   • Encrypting recipient addresses

3. Adds storage slot computation for encrypted outgoing channel information

4. Adds a utility function felt_hex() for formatting field elements as readable hex strings

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This change is 

[m-kus]

• feat(discovery-core): add transfer preflight check #474
• feat(discovery-core): add outgoing state sync orchestrator #473
• feat(discovery-core): add incoming state sync orchestrator #472
• feat(discovery-core): add paginated last-note-index search with bisection #471
• feat(discovery-core): add paginated outgoing channel discovery #470
• feat(discovery-core): paginated notes discovery with nullifier filtering #462
• feat(discovery-core): paginated subchannel discovery with cursor support #461
• feat(discovery-core): paginated incoming channel discovery with cursor support #460
• feat(discovery-core): add iobudget batching, cursor types, and new cost constants #459
• feat(discovery-core): add secretfelt type and unify key param naming #458
• feat(discovery-core): add batch iviews methods and outgoing channel support #457
• feat(discovery-core): add hash primitives and outgoing channel storage slots #456 👈 (View in Graphite)
• chore(claude): move claude.md into .claude and split rules into individual files #455
• refactor(indexer): move devnet dump generation to a separate script, scaffold e2e tests dir #454
• fix(sdk): sync sdk with cairo contract renames (to_addr, enc_user_addr_hash) #469
• main

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[Yoni-Starkware]

@Yoni-Starkware reviewed 4 files and all commit messages, and made 3 comments.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @m-kus).

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crates/discovery-core/src/privacy_pool/hashes.rs line 3 at r1 (raw file):

//! Hash functions and domain separation tags.
//!
//! TODO: rename primitives to match smart contract terminology

Still relevant?

Code quote:

//! TODO: rename primitives to match smart contract terminology

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crates/discovery-core/src/privacy_pool/hashes.rs line 136 at r1 (raw file):

/// Computes the nullifier for a note.
///
/// `nullifier = hash(NULLIFIER_TAG, channel_key, token, index, 0, decryption_key)`

Unnecessary, it just repeats the impl (in all these funcs)

[m-kus]

@m-kus made 1 comment and resolved 1 discussion.
Reviewable status: 3 of 4 files reviewed, 1 unresolved discussion (waiting on @Yoni-Starkware).

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crates/discovery-core/src/privacy_pool/hashes.rs line 3 at r1 (raw file):

Previously, Yoni-Starkware (Yoni) wrote…

Still relevant?

Resolved

[Yoni-Starkware]

@Yoni-Starkware reviewed 4 files and all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @m-kus).